Downdraft furnace



Sept; l5, 1942.

J. R. FELLOWS ET'AL DOWN DRAFT FURNAGE Filed March 6, 1940 2Sheets-Sheet 1 A 4.. d.. ai!

J. R. FELLows Erm. 2,295,781

DOWN DRAFT FURNACE Filed March 6, 1940 2 Sheets-Sheet 2 Fie-z5 WML Sept.l5, 1942:

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Patented Sept. i 5, 1942 nowmmm rUaNAcE :anni nobel-t reno, Urbana, andJohn clem Miles, Chamvllm Ill.. signments, to University of ors, bymeine aslllinois Foundation,

Urbana, lll., a corporation of Illinois Application March 6, 1940,Serial! No. 322,562

z claims. (ci. 11o-24) This invention relates to down-draft furnaces,

or green coal is converted into coke by low temperature carbonization,the volatile matter distilling off and passing under a baille wall andburned without substantial smoke, the temperature necessary forsmokeless combustion being maintained from burning coke, and the oxygenand mixing essential to smokeless combustion being provided by an airstream entering adjacent or through said wall, and so arranged thatlwhen the furnace is recharged with fresh or green coal the coke may beforced down the inclined grate into a coke-burning chamber, the cokeburning as a smokeless fuel while the new charge of coal is being coked.

It is highly desirable and it is also an object of this invention toprovide in such a furnace for the supply of a proper amount of air foreach of the three stages of combustion, preferably from an independentsource or opening, with stackdamper control or other suitable draftregulation.

Another object of the invention is to provide 4 a coking chamber with adouble roof comprising an air passage for the introduction of secondaryair.

A further object of the invention is to provide a novel type of bafflewall separating the upper part of the coking chamber from the upper partof the combustion chamber and so constructed as to form a conduituniting with that in the roof of the coking chamber forconductingsecondary air to that portion of the furnace below the baiile wall.

It is also an object of the invention to provide a grate or grates ofVsuch form and arrangement as to permit proper combustion of the fuelbut less than enough for complete consumption of the fuel thereon duringAthe period required to coke an entire charge of fresh fuel in thecoking chamber.

Other objects and advantages of the invention will readily appear fromthe following description.

Referring to the drawings:

Figure 1 is a longitudinal sectional view of a portionv of a furnaceembodying our invention, diagrammatically shown;

Fig. 2 is a Vvertical sectional view, taken as indicated at line 2 ofFig. 1;

Fig. 3 is a vertical sectional view, taken as indicated-at line 3 ofFig. 1;

Fig. 4 is .a horizontal sectional view, taken as indicated at line 4 ofFig. 1;

Fig. 5 is a front view;

Fig. 6 is a perspective view of grate I8;

`Flg. 7 is a view of the lower end of bale wall I6;

Fig. 8 is a view of another form of grate.

Fig. 9 is a partial sectional view of a modified form of baille wall.

In the preferred form illustrated in Figs. 1-7, inclusive, thedown-draft furnace Il comprises a roof I2 having an opening I3 in theupper, front central portion thereof and an air conduit I4' extendinghorizontally and rearwardly to approximately the mid-portion of saidroof and there connecting with a downwardly extending air conduit orconduits I5 in depending, transversely extending baille wall I6 havingan opening or openings I1 in its lower end, and refractory portion IIa,the lower end ISb thereof serving as an ignition surface. Suitablysupported in said furnace `is a grate I8 having an inclined frontportion I 8a, a second inclined portion I9 rearwardly of said firstinclined portion, shaker- 'grate portions 20 and flat, rear portion 2l,said rear portion supporting a transversely extending, refractory stop26 having a face 26a, preferably inclined and positioned adjacent and tothe rear f the shaker-grate portions 20; said grate, said baiiie walland said stop being so proportioned and disposed as substantially todivide said furnace into four compartments or chambers, namely, a coking-charnberr22, a coke-burning chamber 23, a gas-combustion chamber 24,and an ash receiver 25, so proportioned with respect to each other andto the grate area as to conduce to substantially uniform and smokelessconsump- V tion of the fuel when air is admitted in suitableproportions.

The inclination of the portion I8a of said grate may be of any suitableangle but is preferably of such angle that the coking coal may beconveniently forced downwardly when the coking has vsuicientlyprogressed and green fuel is added.

We have obtained good results with an angle of approximately 20 from thehorizontal. The inclination of the portion I9 of th' grate is preferablysharper, of the order of 45 to 60 from the horizontal, so as to providea chamber or pit 23 beneath the baffle wall I6 for the burning of thecoke formed in the coking chamber 22, and the provision of asubstantially continuous source of heat suitable for igniting the greenfuel in chamber 22 and the heating of the ignition surface lsb.

Baiie wall I6 consists of channel plates 33 supported by an intermediateplate 33a. Plates 33 have rearwardly extending iianged portions 3ft anda suitablydisposed anchoring portion 35 extendingthrough an opening 33oprovided in said intermediate plate 33a and secured thereto by welding ahead 36 on the end of said anchoring portion in position as indicated inFigs. land 4, the rear of said intermediate plate 33a having' suitablydisposed indented portions 33h to seat the heads 36.. The plates 33 arepreferably of special heat resisting material capable of withstanding atemperature of at least 1800" F. We have obtained satisfactory resultswith plates of 28% chromium and 8% nickel cast iron. A. heat resistingalloy also is used in welding the head 36. AThe plates 33 may be of anysuitable dimensions. We have obtained good results using plates of thematerial mentioned approximately 3" wide and 1A" thick, spaced asuitable distance, approximately 1x6" in they example referred to, toallow for expansion.

Supporting plate 33a may be of any suitable material such as 5/8"locomotive iirebox steel. The plate 33a 1s of the same width as thefurnace but is preferably of substantially less depth than the baillewall to avoid exposing its lower portion to intense heat. Plate 33a maybe secured in any suitable manner, by screws, welding, or otherwise, tothe sides or roof of the furnace.

The baiile wall may be supplemented by a refractory block or blocksIlia, which has a cut away portion adapted to t against the rear ofplate 33a and beneath its lower portion as shown in Fig. 1. `The blockida may be of any suitable a refractory block they are preferably ofthey form shown in Fig. 9, the part 33d being disposed beneath thebottom of the supporting plate 33a.

The refractory stop 26 serves to block the coke pushed down from. thecoking chamber and to form one sideof the coke-burning chamber; itsforward surface 26a, especially the upper portion thereof, also servesas a supplemental ignition surface. for mixing and igniting the gas andair passing over it in a manner similar to the lower portion `Ilb of therefractory surface of the baille Wall i6. While it is preferable to useit,

l y stop 2S may be omitted.

The roof I2 may be so formed as to provide a hood I2a over the door 2,said hood having a laterally extending opening B2b in its undersidecommunicating with air passage It and adapted to admit smoke that maybeemitted upon opening the door 2,1; said door 21 having an outwardlyextending horizontal flange 21a across its upper edge adapted to closethe .opening |2-b `when the door is closed.

Air is admitted to the furnace through opening 23 in door 2l and opening30 in door 2@ provided in the front thereof and opening I3 previouslyreferred to in such quantities as may be needed. These openings may beadjustable for various fuels but the adjustment having been determinedfor a given fuel it should remain unchanged to provide for the admissionof relatively xed quantities of air; whatever regulation is requiredbeing provided by damper 32 in stack 3l or other suitable draftregulating means.

The opening 28 is of such size and shape and so placed as to admitsuiiicient air to the coking chamber for coking the coal at a suitablerate butsmall enough to prevent excessive combustion ofv coke in thecoking chamber and thus 'avoid overheating of the materials in thebaille wall. The opening 30 and the openings or perforations in thegrates are of such configuration as to admit a quantity of air suicientfor l maintaining an ignition temperature in the coke thereon at alltimes but insufcient for complete burning out of the coke on the grateduring the period required fully to coke a charge of coal in the cokingchamber. The opening I3, the conduit Id-Iiu and openings I l thereof areof such form and proportions as to provide a stream of air suitable forsubstantially complete combustion of the gases passing beneath the baiiewall and into the gas combustion chamber. As shown the opening i3 is around hole similar to l openings 28 and 30, while the configuration ofopenings Il is indicated in Fig. 7. The advantages of such anarrangement is readily apparent. Especially advantageous is the correctproportioningof the quantities of air admitted to the three stages orphases of combustion, namely, primary air to the coking chamber, primaryair beneath the grate to facilitate the burning of the coke, andsecondary air to mix with the combustible gases beneath the baiile walland facilitate their further combustion; all being more or less directlyrelated to the configuration of the several chambers and the grate andcontributing to the substantially uniform and smokeless consumption ofthe fuel.

The rate of combustion is controlled by regulation of the draft (usuallyby means of a check door in the smoke pipe or stack). With such anarrangement it is possible, by proper apportionment of air, to time theseveral phases of combustion so that, for example, the coke-burningperiod will be approximately the same as lmodate 40 pounds `of greencoal, taking into account the slope of the coal when piled into thecoking chamber and` the waste space resulting, or approximately 2 cubicfeet; the volume of the coke-burning chamber 23 would be approximately 1cubic foot; the volume of the combustion chamber 24, depending on thedesign and arrangement of the heating surface, would be not less thanapproximately 2 cubic feet. For combustion of such a charge of fuel,using Illinois bituminous coal, to the best advantage and withoutsubstantial smoke loss the openings for the admission of air to thefurnace should be approximately as follows: opening I3, one andthreequarters inches in diameter; 28 and 30, each one inch in diameter.Draft available should be approximately 0.12" of water. Openings I8b andIsa in inclined portions I8a and I9 of grate I8 may be of the order of1/3" diameter on 1" cenizontal shaker grate portion 2li.

Instead of the arrangement of grates shown in Q v Fig. 6, an arrangementsuch as that shown in Fig.

8, in which the forward grate has a single inclined portion may beemployed. The openings |817 and lila of grate portions l8r, and i9 maybe omitted, in which case the free area in the grate 2li should beenlarged accordingly.

While not shown in the dras, the side walls of the furnace wouldordinarily be suitably lined with refractory material from the level ofthe grate to a height approximately even with the lower end of thebaille wall i6.

We have used the words coke and coking in describing our invention, notin the limited sense of the terms as applied to the commodity7 known ascoke or making or forming that commodity strictly but in the sense ofthe product resulting when heat is applied to solid fuel and thevolatile matter driven oil therefrom, and the process of making orforming such product Our invention is to be understood as residing inthe method of controlling the combustion` of fuel as herein set forth aswell as in the combi nation, construction and arrangement of par cokingchamber, a coke-burning chamber, a com- 4s bustion chamber, a baillewall between said cokingY chamber and said combustion chamber, the lowerportion of said baille wall forming an ignition sur-1 face above theforward portion of said cokeburning chamber, a vertically extendingconduit through said baille wall having an outlet in the lower portionthereof for introducing secondary air into said furnace downwardly nearthe forward portion of said coke-burning chamber to mix with andfacilitate the combustion of gases emanating primarily from said cochamber and secondarily from said coke-burning chamber., saidcoke-burning chamber being disposed adjacentl to the lower portion ofsaid cclrins chamber so that coke burning in said coke-burning chamberwill provided an ignition surface for gases emanating from the cokingchamber, and means for admitting air'into said furnace beneath thecoke-buming chamber so as to pass upwardly into the bed of coke bgtherein, the parts having' such relative dimensions and being soarranged as to enable the flow of air to the coking chamber and to andbeneath the coke-burning chamber in predetermined proportions and 'toprovide reguable; progressive. substantially smokeless combustion ofsuccessive charges of fuel, proceeding sequentially' through the cokingof one charge con- ,curreutly with the burning ci coke derived from apreceding charge.

2. A down-draft furnace as set forth in claim l, in which the outlet ofthe secondary air conduit is disposed above the rearward portion of theinclined forward grate, the conformation of the structure being such asto provide a stricture between the lower portion of the coking; chamberand the adjacent portion of the coke-burning chamber whereby the fu lcharge is retained in the coking chamber untl coke burning in thecoke-burning chamber is substantially consumed, and the coking oi thefuel in the coking chamber progresses regulably, forwardly and upwardlyfrom said stricture. u

JULIAN ROBERT rsmows. JQHN CIEM

